1. Field of the Invention
The present invention generally relates to a drive shaft that rotates around a shaft axis when transmitting a driving force from a driving source to a driven portion. It also relates to an insertion instrument including such a drive shaft, and an insertion device including such an insertion instrument.
2. Description of the Related Art
International Publication No. 2013/038720 discloses an endoscopic device including an insertion section that extends along the longitudinal axis, and an assistance tool (spiral unit) attached to the insertion section. In this endoscopic device, a drive shaft extends inside the insertion section (tubular section). When a motor (driving source) provided in a held section (operation section) of the endoscope generates a driving force, the drive shaft is rotated around the shaft axis by the driving force transmitted to the drive shaft. When the drive shaft rotates, the driving force is transmitted to a rotor (driven portion) provided in the insertion section, and rotates the rotor around the longitudinal axis. When the rotor rotates in a state that the assistance tool is attached to the insertion section, the assistance tool rotates together with the rotor around the longitudinal axis.